Additives with a reduced tendency to emulsify, which improve the lubricating action of highly desulphurised fuel oils

ABSTRACT

The present invention relates to an additive for improving the lubrication capacity of fuel oils with a maximum sulfur content of 0.035 wt. %. The additive contains at least one ester of a bivalent or polyvalent alcohol and a mixture of unsaturated and optionally saturated fatty acids, whose carbon chain lengths are between 8 and 30 carbon atoms, the aforementioned esters having an OH value of less than 200 mg KOH/g ester and an iodine value greater than 100 g l/100 g ester. The invention also relates to fuel oils with a maximum sulfur content of 0.035 wt. %, which contain the inventive additives. The novel additives exhibit less tendency to emulsify than the additives of the prior art.

Additives with a reduced tendency to emulsify, which improve thelubricating action of highly desulfurized fuel oils.

The present invention relates to additives composed of esters betweenpolyols and fatty acid mixtures, and also to their use for improving thelubricity of highly desulfurized fuel oils coupled with simultaneouslyreduced tendency to emulsify.

Mineral oils and mineral oil distillates which are used as fuel oilsgenerally contain 0.5% by weight or more of sulfur, which causes theformation of sulfur dioxide in the course of combustion. In order toreduce the resulting environmental pollution, the sulfur content of fueloils is being reduced ever further. The standard EN 590 relating todiesel fuels currently prescribes a maximum sulfur content of 350 ppm inGermany. In Scandinavia, fuel oils having fewer than 50 ppm, and inexceptional cases having fewer than 10 ppm, of sulfur are already beingused. These fuel oils are generally produced by refining, underhydrogenating conditions, the fractions obtained from crude oil bydistillation. However, the desulfurization also removes other substanceswhich confer a natural lubricity on the fuel oils. Among others, thesesubstances include polyaromatic and polar compounds.

It has now been found that the friction- and wear-reducing properties offuel oils deteriorate with an increasing degree of desulfurization.These properties are often so inadequate that instances of corrosion areto be expected even after a short time on the materials lubricated bythe fuel, for example the distributor injection pumps of diesel engines.The maximum value for the 95% distillation point of 360° C. laid down byEN 590 since the year 2000 and the further reduction of the 95%distillation point to below 350° C. and sometimes below 330° C. whichhas been undertaken in the meantime in Scandinavia aggravates theseproblems further.

The prior art therefore describes approaches which are intended toprovide a solution to this problem (lubricity additives).

EP-A-0 680 506 discloses that esters of fatty acids confer improvedlubricity to highly desulfurized fuel oils. Particular mention is madeof glycerol monooleate and diisodecyl adipate.

EP-A-0 739 970 discloses the suitability of fatty acid mixtures forimproving the lubricity of low-sulfur fuel oils. Compositions havingdifferent degrees of esterification and different degrees of saturationof the fatty acids are disclosed.

EP-A-0 839 174 discloses fuel oils with improved lubricity which are lowin sulfur and comprise a mixture of polyol esters with unsaturated fattyacids.

However, the fatty acid esters based on commercial fatty acid mixturesof the prior art show a marked tendency to emulsify in the fuel oilsadditized by them. This means that emulsification of the water in thefuel oil takes place on contact of such a fuel oil with water. Theseemulsions to be found in particular on the oil/water phase boundary canonly be removed with great difficulty, if at all. Since these emulsionsas such cannot be used directly as fuel oils, they reduce the value ofthe products. This problem occurs to a particularly high degree whenesters based on natural fatty acid mixtures are used.

It is an object of the present invention to find lubricity-improvingadditives for desulfurized fuel oils which have a reduced tendency toemulsify compared to the prior art.

It has been found that, surprisingly, esters of fatty acid mixtureswhich have a certain combination of hydroxyl number and iodine number donot have the emulsifiability of the esters of the prior art, and haveexcellent lubricity in desulfurized fuel oils. It is presumed that thereduced tendency to emulsify is brought about by two effects: firstly,the polarity range of the additives, which is determined by the OHnumber, brings about a reduced affinity of the amphiphilic activeingredients for water. Secondly, the formation of micellar,surface-active structures is simultaneously disrupted by the number ofdouble bonds in the alkyl radicals, which is defined by means of theiodine number.

The present invention therefore provides an additive for improving thelubricity of fuel oils having a maximum sulfur content of 0.035% byweight, comprising at least one ester of a di- or polyhydric alcohol anda mixture of unsaturated and optionally saturated fatty acids whosecarbon chain lengths are between 8 and 30 carbon atoms, the estersmentioned having an OH number of below 200 mg KOH/g of ester and aniodine number of more than 100 g of I/100 g of ester.

The invention further provides fuel oils having a maximum sulfur contentof 0.035% by weight which comprise the additives according to theinvention.

The invention further provides the use of the additives according to theinvention for improving the lubricity of fuel oils having a sulfurcontent of at most 0.035% by weight.

The invention further provides a process for improving the lubricity offuel oils having a maximum sulfur content of 0.035% by weight, by addingthe additive according to the invention to the fuel oils.

Preferred fatty acids which are a constituent of the fatty acid mixtureare those having from 10 to 26 carbon atoms, in particular from 12 to 22carbon atoms. The alkyl radicals of the fatty acids consistsubstantially of carbon and hydrogen. However, they may also contain asfurther constituents, for example, hydroxyl, halogen, amino or nitrogroups, as long as they do not impair the predominant hydrocarboncharacter. The fatty acids present in the fatty acid mixture preferablycontain at least one double bond. They may contain a plurality of doublebonds, for example two or three double bonds, and be of natural orsynthetic origin. In the case of polyunsaturated carboxylic acids, theirdouble bonds may be isolated or else conjugated. In preferred fatty acidmixtures, at least 50% by weight, in particular at least 75% by weight,especially at least 90% by weight, of the fatty acids contain one ormore double bonds. The iodine numbers of the parent fatty acids of theesters according to the invention are preferably between 105 and 190 g,in particular from 110 to 180 g and especially from 120 to 180 g, ofI/100 g of ester.

Suitable fatty acid mixtures contain at least two unsaturated fattyacids having from 10 to 26 carbon atoms. Suitable unsaturated fattyacids are, for example, oleic acid, erucic acid, palmitoleic acid,myristoleic acid, linoleic acid, linolenic acid, elaeosteric acid,arachidonic acid and/or ricinoleic acid. Preference is given inaccordance with the invention to using fatty acid mixtures or fractionsobtained from natural fats and oils, for example peanut oil fatty acid,fish oil fatty acid, linseed oil fatty acid, palm oil fatty acid,rapeseed oil fatty acid, ricenic oil fatty acid, castor oil fatty acid,colza oil fatty acid, soya oil fatty acid, sunflower oil fatty acid andtall oil fatty acid, each of which have appropriate iodine numbers.

In addition, the fatty acid mixtures may contain minor amounts, i.e. upto 10% by weight, preferably less than 5% by weight, especially lessthan 2% by weight, of saturated fatty acids, for example lauric acid,tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid,margaric acid, stearic acid, isostearic acid, arachic acid and behenicacid.

Likewise suitable as a constituent of the fatty acid mixtures aredicarboxylic acids such as dimerized fatty acids and alkyl- andalkenylsuccinic acids having C₈-C₅₀-alk(en)yl radicals, preferablyhaving C₈-C₄₀-alkyl radicals, in particular having C₁₂-C₂₂-alkylradicals. The alkyl radicals may be either linear or branched(oligomerized alkenes, PIB). Preference is given to proportions of up to10% by weight, in particular less than 5% by weight. The fatty acids mayalso contain 1-40% by weight, especially 1-25% by weight, in particular1-5% by weight, of resin acids.

Suitable alcohols contain preferably from 2 to 6, in particular from 3to 4, carbon atoms, and from 2 to 5, in particular from 3 to 4, hydroxylgroups, but a maximum of one hydroxyl group per carbon atom.Particularly suitable alcohols are ethylene glycol, diethylene glycol,propylene glycol, glycerol and pentaerythritol.

The esters can be prepared from alcohols and fatty acids in a knownmanner by esterification. As an alternative, it is also possible topartially hydrolyze naturally occurring fats and oils. Esters accordingto the invention are those which can be prepared from a di- orpolyhydric alcohol and a mixture of fatty acids. These include bothmixtures, for example, of monoesters of an alcohol with different fattyacids, of monoesters of different alcohols with different fatty acids,and mixtures of mono-, di- and/or triesters, or optionally higheresters, of one or more alcohols with different fatty acids. Esters arein accordance with the invention when they can be prepared from a fattyacid mixture.

The iodine numbers of the esters according to the invention arepreferably between 100 and 180 g, in particular from 110 to 150 g, ofI/100 g of ester. The iodine numbers result from the iodine number ofthe parent fatty acid mixture and the alcohol used for theesterification in a stoichiometric manner.

The OH number of the esters in the additive according to the inventionis preferably between 110 and 195, in particular between 130 and 190 mgKOH/g of ester. In general, these are mixtures of different esters, forexample mixtures of mono-, di- and triglycerides, mixtures as occur inthe esterification of polyols.

The additives according to the invention are added to oils in amounts offrom 0.001 to 0.5% by weight, preferably from 0.005 to 0.3% by weightand especially from 0.01 to 0.1% by weight. They may be used as such orelse dissolved in solvents, for example aliphatic and/or aromatichydrocarbons or hydrocarbon mixtures, for example toluene, xylene,ethylbenzene, decane, pentadecane, benzine fractions, kerosene orcommercial solvent mixtures, such as Solvent Naphtha, ®Shellsol AB,®Solvesso 150, ®Solvesso 200, and ®Exxsol, ®Isopar and ®Shellsol Dtypes. The additives according to the invention preferably contain1-80%, especially 10-70%, in particular 25-60%, of solvent. Theadditives, which may be used without difficulty even at low temperaturesof, for example, −30° C. and lower, improve the lubricity of theadditized oils with simultaneously reduced tendency to emulsify.

To prepare additive packages for specific solutions to problems, theadditives according to the invention may also be used together with oneor more oil-soluble coadditives which in themselves improve thelubricity and/or cold-flow properties of crude oils, lubricant oils orfuel oils. Examples of such coadditives are vinyl acetate-containingcopolymers or terpolymers of ethylene, paraffin dispersants, combpolymers, alkylphenol-aldehyde resins and also oil-soluble amphiphiles.

For instance, mixtures of the additives according to the invention withcopolymers which contain from 10 to 40% by weight of vinyl acetate andfrom 60 to 90% by weight of ethylene have been found to be outstandinglyuseful. In a further embodiment of the invention, the additivesaccording to the invention are used in a mixture with ethylene/vinylacetate/vinyl neononanoate terpolymers or ethylene/vinyl acetate/vinylneodecanoate terpolymers to simultaneously improve the flowability andlubricity of mineral oils or mineral oil distillates. Apart fromethylene, the terpolymers of vinyl neononanoate or vinyl neodecanoatecontain from 10 to 35% by weight of vinyl acetate and from 1 to 25% byweight of the particular neo compound. In addition to ethylene and from10 to 35% by weight of vinyl esters, further preferred copolymers alsocontain from 0.5 to 20% by weight of olefin such as diisobutylene,4-methylpentene or norbornene. The mixing ratio of the additivesaccording to the invention with the above-described ethylene/vinylacetate copolymers or the terpolymers of ethylene, vinyl acetate and ofvinyl esters of neononanoic acid or of neodecanoic acid (in parts byweight) is from 20:1 to 1:20, preferably from 10:1 to 1:10.

For use as a flow improver and/or lubricity additive, the reactionproducts according to the invention may also be used together withparaffin dispersants. Paraffin dispersants reduce the size of theparaffin crystals and have the effect that the paraffin particles do notsettle, but rather remain dispersed colloidally with a distinctlyreduced tendency to sedimentation. In addition, they reinforce thelubricity of the additives according to the invention. Useful paraffindispersants have been found to be oil-soluble polar compounds havingionic or polar groups, for example amine salts and/or amides, which areobtained by reacting aliphatic or aromatic amines, preferably long-chainaliphatic amines, with aliphatic or aromatic mono-, di-, tri- ortetracarboxylic acids or their anhydrides (cf. U.S. Pat. No. 4,211,534).Other paraffin dispersants are copolymers of maleic anhydride andα,β-unsaturated compounds which may optionally be reacted with primarymonoalkylamines and/or aliphatic alcohols (cf. EP 0 154 177), thereaction products of alkenyl-spiro-bislactones with amines (cf. EP 0 413279 B1) and, according to EP 0 606 055 A2, reaction products ofterpolymers based on α,β-unsaturated dicarboxylic anhydrides,α,β-unsaturated compounds and polyoxyalkylene ethers of lowerunsaturated alcohols. Alkylphenol-aldehyde resins are also suitable asparaffin dispersants.

For instance, the additives according to the invention may be used in amixture with alkylphenol-formaldehyde resins. In a preferred embodimentof the invention, these alkylphenol-formaldehyde resins are those of theformula

where R^(A) is C₄-C₅₀-alkyl or alkenyl, R^(B) is ethoxy and/or propoxy,n is a number from 5 to 100 and p is a number from 0 to 50.

Finally, in a further embodiment of the invention, the additivesaccording to the invention are used together with comb polymers. Thisrefers to polymers in which hydrocarbon radicals having at least 8, inparticular at least 10, carbon atoms are bonded to a polymer backbone.These are preferably homopolymers whose alkyl side chains have at least8 and in particular at least 10 carbon atoms. In copolymers, at least20%, preferably at least 30%, of the monomers have side chains (cf.Comb-like Polymers-Structure and Properties; N. A. Platé and V. P.Shibaev, J. Polym. Sci. Macromolecular Revs. 1974, 8, 117 ff). Examplesof suitable comb polymers are, for example, fumarate/vinyl acetatecopolymers (cf. EP 0 153 176 A1), copolymers of a C₆-C₂₄-α-olefin and anN-C₆-C₂₂-alkylmaleimide (cf. EP 0 320 766), and also esterifiedolefin/maleic anhydride copolymers, polymers and copolymers of α-olefinsand esterified copolymers of styrene and maleic anhydride.

Comb polymers can be described, for example, by the formula

In this formula:

A is R′, COOR′, OCOR′, R″—COOR′ or OR′;

D is H, CH₃, A or R;

E is H or A;

G is H, R″, R″—COOR′, an aryl radical or a heterocyclic radical;

M is H, COOR″, OCOR″, OR″ or COOH;

N is H, R″, COOR″, OCOR, COOH or an aryl radical;

R′ is a hydrocarbon chain having 8-150 carbon atoms;

R″ is a hydrocarbon chain having from 1 to 10 carbon atoms;

m is a number between 0.4 and 1.0; and

n is a number between 0 and 0.6.

The mixing ratio (in parts by weight) of the additives according to theinvention with resins or comb polymers is in each case from 1:10 to20:1, preferably from 1:1 to 10:1.

The additives according to the invention are particularly well suited touse in middle distillates. Middle distillates refer in particular tothose mineral-oils which are obtained by distillation of crude oil andboil in the range from 120 to 450° C., for example kerosene, jet fuel,diesel and heating oil. The oils can also contain alcohols such asmethanol and/or ethanol or consist of these. The additives according tothe invention are preferably used in those middle distillates whichcontain fewer than 350 ppm of sulfur, in particular fewer than 200 ppmof sulfur and in special cases fewer than 50 ppm of sulfur. These aregenerally those middle distillates which have been subjected to refiningunder hydrogenating conditions, and therefore only contain smallfractions of polyaromatic and polar compounds which confer a naturallubricity on them. The additives according to the invention are alsopreferably used in those middle distillates which have 95% distillationpoints below 370° C., in particular 350° C. and in special cases below330° C. They can also be used as components in lubricant oils.

The mixtures can be used alone or else together with other additives,for example with pour point depressants or dewaxing assistants, withcorrosion inhibitors, antioxidants, sludge inhibitors, dehazers,conductivity improvers, lubricity additives, and additives for reducingthe cloud point. They are also used successfully together with additivepackages which contain, inter alia, known ashless dispersant additives,detergents, antifoams, and corrosion inhibitors. The synergisms whichare described in the prior art are achieved between the additivesaccording to the invention and the further additives mentioned withregard to cold-flow properties in accordance with WO-95/03377 andlubricity in accordance with WO-96/18708 and WO-96/23855.

The effectiveness of the additives according to the invention aslubricity additives is illustrated in detail by the examples whichfollow.

EXAMPLES

TABLE 1 Characterization of the additives used (inv = inventive, C =comparative) Iodine OH number number Additive [mg KOH/g] [g l/100 g]Chemical characterization A (inv) 158 103 partial ester of glycerol andsoya oil fatty acid B (C) 181 52 partial ester of glycerol and tallowfatty acid C (C) 153 76 partial ester of glycerol and olein D (inv) 88116 partial ester of glycerol and tall oil fatty acid E (inv) 193 122partial ester of glycerol and tall oil fatty acid F (C) 278 77 partialester of glycerol and olein

The OH numbers are determined to DIN 53240 by reacting with a definedexcess amount of acetic anhydride and subsequently titrating the aceticacid formed.

Iodine numbers are determined according to Kaufmann. To this end, asample of known mass is admixed with a defined, excess amount of amethanolic bromine solution, and an amount of bromine which isequivalent to the content of double bonds in the sample is added on tothe double bonds. The excess of bromine is back-titrated using sodiumthiosulfate.

TABLE 2 Esters according to the prior art (comparative values) OH numberIodine number Ester [mg KOH/g] [g l/100 g] Glycerol monooleate (pure)315 71 Glycerol dioleate (pure) 90 82 EP 0 839 174, Ex. A 181 78 EP 0839 174, Ex. B 315 71 EP 0 839 174, Ex. C 317 143 EP 0 739 970, Ex. A181 77 EP 0 739 970, Ex. G 284 120 EP 0 739 970, Ex. H 141 44 EP 0 739970, Ex. I 155 72 EP 0 739 970, Ex. J 111 74 EP 0 739 970, Ex. K 185 78EP 0 739 970, Ex. L 122 81 EP 0 739 970, Ex. M 192 77 EP 0 739 970, Ex.N 8 86 EP 0 739 970, Ex. O 84 75 EP 0 739 970, Ex. P 227 76 EP 0 739970, Ex. Q 184 73 EP 0 739 970, Ex. R 192 62

Tendency to emulsify in middle distillates

The tendency of additives to emulsify is tested to ASTM D 1094-85. 80 mlof a diesel fuel are admixed in a 100 ml measuring cylinder with 250 ppmof the additive to be tested, and heated at 60° C. and agitated for 15minutes. After cooling to room temperature, 2 ml of buffer solution areadded and the mixture is agitated for 2 minutes. After 5 minutes, thesample is assessed visually by the following criteria:

Assessment of the separation layer Assessment of the phase separation 1clear and clean 1 complete absence of any 1b small, clear bubbles whichare emulsions and/or deposits in estimated to cover not more both phasesor on the top of than 50% of the separation the oil phase. layer. Nostreaks, no film 2 as (1), but additionally formation or other wettingsmall air bubbles or small at the separation layer. water droplets inthe oil 2 streaks, film formation or phase. other wetting at the 3emulsions and/or deposits in separation layer both phases or on the topof 3 narrow border or slight foam the oil phase, and/or formation, orboth drops in the water phase 4 thick border or extensive foam oradhering to the formation, or both wall (excluding the wall above theoil phase). In brackets: amount of the water phase

TABLE 3 Tendency of the additives to emulsify Separation Phase Oil WaterExample Additive layer separation phase phase 1 A 1b 2 (20 ml H₂O)slightly clear cloudy 2 (C) B 3 3 (8 ml H₂O) cloudy clear 3 (C) C 4 3(10 ml H₂O) cloudy clear 4 D 2 2 (20 ml H₂O) slightly clear cloudy 5 E 22 (20 ml H₂O) slightly clear cloudy 6 (C) F 3 3 (6 ml H₂O) cloudy clear

Lubricity in Middle Distillates

The lubricity of the additives was carried out on additized oils at 60°C. by means of an HFRR instrument from PCS Instruments. The highfrequency reciprocating rig test (HFRR) is described in D. Wei, H.Spikes, Wear, Vol. 111, No. 2, p. 217, 1986. The results are quoted asthe coefficient of friction and wear scar (WS 1.4). A low coefficient offriction and a low wear scar indicate good lubricity.

The test oil used was a Scandinavian winter diesel having the followingcharacteristics:

Boiling range: 185–320° C. Density: 0.820 g/cm³ Cloud point: −29° C.Sulfur content: 3 ppm

The boiling parameters are determined to ASTM D-86 and the cloud pointis determined to ISO 3015.

TABLE 4 Wear scar in test oil 2 Example Additive Dosage Wear scarFriction  7 (C) none — 679 μm 0.40  8 (C) glycerol monooleate 100 ppm230 μm 0.13 (99%)  9 (C) glycerol dioleate 100 ppm 306 μm 0.16 10 A 100ppm 210 μm 0.12 11 (C) B 100 ppm 263 μm 0.14 12 (C) C 100 ppm 284 μm0.14 13 D 100 ppm 206 μm 0.12 14 E 100 ppm 301 μm 0.14 15 (C) F 100 ppm291 μm 0.13

1. A fuel oil having a maximum sulfur content of 0.035% by weight,comprising an additive comprising at least one ester of a di- orpolyhydric alcohol and a mixture comprising unsaturated fatty acidshaving carbon chain lengths between 8 and 30 carbon atoms, saidunsaturated fatty acids selected from the group consisting of oleicacid, erucic acid, palmitoleic acid, myristoleic acid, linoleic acid,linolenic acid, elaeosteric acid, arachidonic acid, ricinoleic acid andmixtures thereof, the at least one ester having an OH number of between110 and 195 mg KOH/g of ester and an iodine number of more than 100 g ofl/100 g of ester, in amounts of from 0.001 to 0.5% by weight based onthe fuel oil.
 2. A fuel oil as claimed in claim 1, wherein the iodinenumber is between 100 and 180 g of l/100 g of ester.
 3. The fuel oil ofclaim 1, wherein said unsaturated fatty acids have from 10 to 26 carbonatoms.
 4. The fuel oil of claim 1, wherein the mixture comprising saidunsaturated fatty acids further comprises less than 10% by weight ofsaturated fatty acids.
 5. The fuel oil of claim 1, wherein the di- orpolyhydric alcohol contains from 2 to 6 carbon atoms.
 6. The fuel oil ofclaim 1, wherein the di- or polyhydric alcohol contains from 2 to 5hydroxyl groups, said alcohol having a maximum of one hydroxyl group percarbon atom.
 7. The fuel oil of claim 1, wherein the mixture of saidunsaturated fatty acids comprises dicarboxylic acids.
 8. The fuel oil ofclaim 1, further comprising an alkylphenol-formaldehyde resin present inan additive:resin ratio of from 1:10 to 20:1 by weight.
 9. The fuel oilof claim 1, further comprising a copolymer or terpolymer selected fromthe group consisting of a copolymer containing from 10 to 40% by weightof vinyl acetate and from 60 to 90% by weight of ethylene, anethylene/vinyl acetate/vinyl neononanoate terpolymer or anethylene/vinyl acetate/vinyl neodecanoate terpolymer which, apart fromethylene, said terpolymer contains from 10 to 35% by weight of vinylacetate and from 1 to 25% by weight of said neo compound, a copolymerwhich, in addition to ethylene and from 10 to 35% by weight of vinylesters, also contains from 0.5 to 20% by weight of olefin, and mixturesthereof present in a mixing ratio of additive to the above-describedcopolymer or terpolymer (in parts by weight) of from 20:1 to 1:20. 10.The fuel oil of claim 1, further comprising oil-soluble polar compoundshaving ionic or polar groups which are obtained by reacting aliphatic oraromatic amines with an aliphatic or aromatic carboxylic acid oranhydride selected from the group consisting of mono-, di-, tri-, tetraand mixtures thereof.
 11. The fuel oil of claim 1, further comprisingcomb polymers of the formula

where A is R′, COOR′, OCOR′, R″-COOR′ or OR′; D is H, CH₃, A or R; E isH or A; G is H, R″, R″-COOR′, an aryl radical or a heterocyclic radical;M is H, COOR″, OCOR″, OR″or COOH; N is H, R″, COOR″, OCOR, COOK or anaryl radical; R′ is a hydrocarbon chain having from 8-150 carbon atoms;R″ is a hydrocarbon chain having from 1 to 10 carbon atoms; m is anumber between 0.4 and 1.0; and n is a number between 0 and 0.6 whereinsaid comb polymers are present in a mixing ratio (in parts by weight) ofadditives to comb polymers of from 1:10 to 20:1.
 12. The fuel oil ofclaim 1, further comprising copolymers of maleic anhydride and α,β-unsaturated compounds which may optionally be reacted with primarymonoalkylamines and/or aliphatic alcohols are additionally present. 13.The fuel oil of claim 1, further comprising reaction products ofalkenyl-spiro-bislactones with amines.
 14. The fuel oil of claim 1,wherein reaction products of terpolymers based on α, β-unsaturateddicarboxylic anhydrides α, β-unsaturated compounds and polyoxyalkyleneethers of lower unsaturated alcohols are additionally present.
 15. Aprocess for improving the lubricity of fuel oils having a sulfur contentof at most 0.035% by weight, said process comprising adding to said fueloil an additive comprising at least one ester of a di- or polyhydricalcohol and a mixture comprising unsaturated fatty acids having carbonchain lengths between 8 and 30 carbon atoms, said unsaturated fattyacids selected from the group consisting of oleic acid, erucic acid,palmitoleic acid, myristoleic acid, linoleic acid, linolenic acid,elaeosteric acid, arachidonic acid, ricinoleic acid, and mixturesthereof, the said ester having an OH number of between 110 and 195 mgKOH/g of ester and an iodine number of more than 100 g of I/100 g ofester, in amounts of from 0.00 1 to 0.5% by weight based on the fueloil.
 16. The fuel oil of claim 1, wherein the mixture comprisingunsaturated fatty acids is selected from the group consisting of peanutoil fatty acid, fish oil fatty acid, linseed oil fatty acid, palm oilfatty acid, rapeseed oil fatty acid, ricenic oil fatty acid, castor oilfatty acid, colza oil fatty acid, soya oil fatty acid, sunflower oilfatty acid, tall oil fatty acid, and mixtures thereof.